A technique that determines the state of eyes based on a face image for monitoring the direction of gaze of a person and presuming his/her arousal level is known. In order to determine the state of the eyes, the eyes should be detected accurately in the face image. Further, when determining the driver's state, a face feature point should be detected in real-time.
For example, a technique that extracts a driver's eye position to detect lowering of the arousal level is disclosed in JP 7-181012A. In the process using the technique, an eye presence region is set in a first image frame. Width and length of a region where an eye is present is determined based on a center position of each eye. Then, mask processing is performed from the next frame using the eye presence region, and the eye is extracted as a label which is not in contact with the frame of the eye presence region. Follow-up conducted in the eye presence region limits an extraction range, thereby conducting the extraction at high speeds.
Further, a technique for suppressing influence of lighting conditions or individual differences in facial structure and the like in eye blinking detection is disclosed in JP 7-313459A. The technique disclosed in JP 7-313459A calculates a point P whose edge value is a positive local maximum point and a point M whose edge value is a negative local minimum point (the absolute value of the point M is large) in a one dimensional edge image. Then, initial positions of the search, i.e. points P0 and M0, are determined. The search is conducted to detect extreme points located at an outer side from each initial position and the respective search regions are set accordingly. Hence, the search proceeds upward for detecting the positive extreme points and proceeds downward for detecting the negative extreme points. Then, the check is conducted to determine whether a sign of the edge value is inverted in the search region. The edge value is negative between the point MO and the point M1. Thus, the points P1 and M1 are set as new initial positions and the search is iteratively conducted. No other edge extreme point exists at an upper side of the point P1 and a lower side of the point M1. Hence, the point P1 is set as boundary point A and the point M1 is set as boundary point B. A distance between the boundary point A and the boundary point B is measured to be output as an opening degree of an eyelid.
In the technique disclosed in JP 7-181012A, the mask processing and labeling are performed on a predetermined region, which is not in contact with a subject to be extracted, in a binarized image. However, when using the technique that binarizes the image, the feature point of the subject may not be accurately detected due to the lighting conditions and the individual differences in the facial structure.
Further, the technique disclosed in JP 7-313459A, candidates for the subject to be detected, are extracted from the extreme points on plural base lines. The extraction is conducted based on the extreme values indicating gray level change in the one dimensional edge image. Thus, when detecting an eye, moles and the like are erroneously extracted as the candidates, and the detection result is subject to the influence of the individual differences in the facial structure.
A need thus exists to provide an eye detection apparatus which is not susceptible to the drawback mentioned above.